The conventional electronic apparatus are mostly equipped with one or more typical plane input apparatus, such as a keyboard, a hand writing pad, a plane touching panel, or an input apparatus requiring an operational plane, such as a mouse or a trackball. Among the smaller handheld electronic apparatus, however, space is often inadequate for users to operate along with the conventional plane input apparatus as described above. With electronic devices, such as PDA (personal digital assistant) and cellular phones becoming more powerful and more compact, machine-user interface is always a challenge. A conventional solution is to provide touch panels through viewable screen such as touch pads, e-books, or e-papers.
A problem associated with a conventional plane input device or a typical touch pad is that the user's hand and fingers obscure user's ability to see the screen when the user tries to touch the pad. For example, selecting text using a finger over a portable screen can be cumbersome. Also, human hands are capable of moving in a three-dimensional space, while a conventional human-machine interface device is typically only one-dimensional.